Nanostructured LaFeO₃ Photocathodes with Onset Potentials for the Hydrogen Evolution Reaction Over 1.4 V vs. RHE

Abstract

The photoelectrochemical properties of phase-pure LaFeO 3 (LFO) nanostructured films are investigated upon modification with a thin TiO 2 film and Pt nanoparticles as a catalyst. LaFeO 3 with crystallite domains in the range of 60 nm are prepared by thermolysis of an ionic-liquid precursor and subsequently deposited onto FTO electrode by spin-coating. Deposition of a TiO 2 layer by solutionbased methods leads to the formation of a heterojunction, attenuating dark current associated with hole-transfer (water oxidation) at potential above 1.4 V. The LFO/TiO 2 heterojunction features photocurrent onset potential for the hydrogen evolution reaction of 1.47 V vs. the reversible hydrogen electrode (RHE), which is one of the most positive values reported for a single absorber. Deposition of Pt nanoparticles at the LFO/TiO 2 heterostructure generates a significant increase in the HER photocurrent, although bulk recombination remains an important challenge in these constructs.

Strategies for the deposition of LaFeO3 photocathodes: improving the photocurrent with a polymer template

“…31 However, recent efforts have been made to reduce this effect for LFO lms by incorporating a thin TiO 2 hole blocking layer. 38 PEC measurements of all the LFO samples exhibit a large dark current at potentials below +0.4 V RHE . This can be attributed to oxygen reduction on the areas of exposed FTO 48 and on LFO.…”

“…31 Recent work has been done in avoiding this detrimental hole transfer to the electrolyte in LFO lms by incorporating a TiO 2 blocking layer. 38 It is also important to consider the role that the thickness of LFO lms have on PEC properties. For instance, it has been shown that with increasing lm thickness, a shi from oxidative to reductive behavior is observed due to differing band offsets.…”

PrFeO3 Photocathodes Prepared Through Spray Pyrolysis

“…In this case, holes can accumulate at the semiconductor/electrolyte interface and take part in the oxygen evolution reaction (OER), increasing majority carrier losses. To combat this a hole‐blocking layer could be employed . Despite this observed vast reduction in photocurrent on purging the electrolyte with N 2, we were able to detect H 2 over a 6 h period with constant light illumination (Figure S8).…”

High Interfacial Hole‐Transfer Efficiency at GaFeO3 Thin Film Photoanodes

“…Band alignment of GFO band edges with respect to common electron transport layer (ETL) [44] and hole transport layer (HTL). [44] Band offset with other Fe-based photoelectrodes including LaFeO 3 (LFO), [16] YFeO 3 (YFO), [17] BiFeO 3 (BFO), [45] CaFe 2 O 4 (CaFO), [46] CuFeO 2 (CuFO), [47] ZnFe 2 O 4 (ZFO), [48] and Fe 2 O 3 [49] illustrates how positive is the VBM in GFO. where W is the width of the space charge region, and L n is the holes diffusion length.…”

“…[ 9 ] Other ferrite photoanodes include ZnFe 2 O 4 , MgFe 2 O 4 , and CuFe 2 O 4 , achieving external quantum efficiency values of close to 10% and photocurrent onset potentials ranging from 0.6 up to 1 V. [ 10,11 ] Ferrite photocathodes such as LaFeO 3 and YFeO 3 have shown very interesting photovoltages for the hydrogen evolution reaction, but their activity is limited by bulk and surface recombination losses. [ 12–17 ] Ferroelectric materials such as BiFeO 3 and Bi 2 FeCrO 6 show complex PEC properties that have been linked to ferroelectric domains. [ 18,19 ] For instance, BiFeO 3 exhibits both n‐ and p‐type conductivity, including above photovoltages larger than the bandgap.…”